The invention relates to a solid-state trip device of a molded case electrical circuit breaker having per pole a pair of contacts, elastically urged into contact in the closed position of the circuit breaker and capable of separating by the action of an automatic operating mechanism on a fault, comprising sensors which generate fault signals which are a function of the currents flowing in the conductors protected by the circuit breaker, and a processing unit to which said fault signals are applied to generate a circuit breaker tripping order, when preset thresholds are exceeded, said order being time-delayed according to the value of the fault signals.
The contacts of an electrical circuit breaker must open cleanly to avoid any intermediate contact repulsion position, the contacts nevertheless being insufficiently separated for the arc drawn between the contacts to be extinguished. Continuance of the arc between the partially open contacts causes overheating and damage to the circuit breaker. Repulsion of the contacts takes place due to the effect of the electrodyanmic forces when the current exceeds a preset repulsion threshold, this threshold depending on the configuration of the current in the circuit breaker and on the pole setting characteristics.
To be sure that a circuit breaker does not remain in an intermediate contact repulsion position, the tripping threshold on a fault is generally set to a value lower than that of the repulsion threshold. It is difficult and costly to achieve circuit breakers having perfectly defined repulsion and tripping threshold 20 to 50% lower than the repulsion threshold is frequently selected, which results in a considerable loss of selectivity.
The object of the present invention is to achieve a trip device whose tripping threshold and the repulsion threshold are the same.
Another object of the invention is to achieve a trip device providing instantaneous tripping when the circuit breaker detects a fault.